Soluble aromatic polyimides with high glass transition temperature from benzidine containing tert-butyl groups

A series of soluble polyimides with high glass transition temperature (T _g ) were prepared from four commercial aromatic dianhydrides (i.e., BPDA, OPDA, 6FDA and BPADA) with a rigid aromatic diamine containing tert-butyl groups (3,3′-di-tert-butylbenzidine) (1). The number-average molecular weights of them were in the range from 4.21?×?10⁴ to 1.25?×?10⁵ with the polydispersity indexes between 2.34 and 3.04 by means of gel permeation chromatography relative to a polystyrene standard. They were able to form transparent, flexible and tough films by polymer solution casting. The transmittance of them was higher than 90 % in a wavelength range of 400–700 nm by UV–vis measurement. The XRD results demonstrated that they were amorphous glassy polymers. Except for polyimide 1-BPADA, the T _g s of the rest were higher than 330 °C, and especially the T _g of polyimide 1-BPDA reached up to 375 °C. They did not show appreciable decomposition up to 500 °C under a nitrogen atmosphere, in other words, the 5 % weight losses of them were in the range from 508 to 523 °C. Most of them exhibited high tensile strength and modulus with a low elongation at break at room temperature. They are potential candidates for high performance materials.